Which diagnostic approach is used to confirm diphtheria?

Which diagnostic approach is used to confirm diphtheria?

• A. Blood culture
• B. PCR to confirm (isolate until 3 negative pharyngeal cultures)
• C. Urine antigen test
• D. Sputum culture

Answer: (B)

Confirming diphtheria hinges on proving the organism can produce diphtheria toxin. The toxin is what drives the illness, so identifying a toxigenic strain is essential rather than just finding Corynebacterium diphtheriae. A throat or pharyngeal swab is used to isolate C. diphtheriae, but the crucial step is demonstrating toxigenicity. PCR testing for the tox gene directly confirms that the isolate has the toxin gene and is capable of producing toxin, providing rapid and specific confirmation of diphtheria. If toxin production is shown (or demonstrated by toxin assays on culture), it supports the diagnosis in the appropriate clinical and epidemiologic context. In contrast, blood cultures, urine antigen tests, or sputum cultures do not reliably confirm diphtheria. The infection is localized to the pharynx and mediated by toxin rather than circulating in the blood, and urine or sputum testing is not the standard method for confirming diphtheria.

Confirming diphtheria hinges on proving the organism can produce diphtheria toxin. The toxin is what drives the illness, so identifying a toxigenic strain is essential rather than just finding Corynebacterium diphtheriae.

A throat or pharyngeal swab is used to isolate C. diphtheriae, but the crucial step is demonstrating toxigenicity. PCR testing for the tox gene directly confirms that the isolate has the toxin gene and is capable of producing toxin, providing rapid and specific confirmation of diphtheria. If toxin production is shown (or demonstrated by toxin assays on culture), it supports the diagnosis in the appropriate clinical and epidemiologic context.

In contrast, blood cultures, urine antigen tests, or sputum cultures do not reliably confirm diphtheria. The infection is localized to the pharynx and mediated by toxin rather than circulating in the blood, and urine or sputum testing is not the standard method for confirming diphtheria.